New findings are adding to the research suggesting that more than ever before, what and how much we drink may increase calorie intake and weight without our noticing.

The problem of increasing waistlines and obesity in the United States has escalated in the last 30 years. During this time, calorie consumption increased an average of 150 to 300 calories per day, with about half that increase coming from beverages. The variety of calorie-dense beverages and number of soft-drink servings per day both grew. Average soft drink portion size increased more than 50 percent from about 13 ounces to almost 20 ounces.

Several studies peg calories from beverages as one of the causes of increased numbers of overweight and obese people in the United States. Studies suggest that when people consume more calories from beverages, they don’t compensate by eating or drinking less.

One new study, for example, served 33 men and women the same lunch once a week for six weeks with only the beverage type or amount changing each week. Regardless of the type of beverage, people drank more when served 18 ounces than when served 12 ounces. When the amount of calorie-containing cola increased, women’s beverage calories increased by 10 percent and the men’s by 26 percent.

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Participants ate the same amount of food independent of the higher amount of calories they drank, leading to an increase in the meal’s total calories. Yet after a higher-calorie meal containing sweetened soft drinks, participants reported no difference in hunger or satisfaction.

Gulping down large amountsShort-term studies — generally one to three days — in which people decrease high-calorie soft drink consumption usually show a decreased total daily calorie consumption. Longer term studies ranging from six months to four years have found an association between drinking less calorie-containing soft drinks and weight loss.

Scientists offer several explanations as to why we may not notice calories from some beverages. A drink’s rapid passage through the mouth provides less time for signals to trigger the brain that you are eating. Compared to beverages, solid food seems to provide more of a feeling of fullness, which signals the brain to stop eating. Thick liquids (like smoothies and shakes) provide considerably more fullness signals than thin liquids, such as soft drinks, fruit drinks and sweetened tea and coffee.

As portion sizes of calorie-dense beverages increase, it is easier to gulp down larger amounts than to eat larger portions of solid foods. Finally, some researchers suggest that there may be a psychological component, too. Many of us consider beverages a separate category that does not “count” in the same way as solid food.

For people who either have trouble getting enough or limiting calories, this research suggests that beverage choice and portion are important considerations. Calorie-rich drinks offer an opportunity to boost calories without reducing appetite.

However, for those who look at drinks as a way to work in meals on the run, it suggests that this approach may lead to a higher calorie intake than chewing a meal. For weight control, limiting calorie-containing beverages to a few modest daily servings of nutrient-containing drinks and drinking water, unsweetened tea or coffee and other zero-calorie drinks is a smart strategy.